1. Technical Field
Improved positive displacement pumps are disclosed. More specifically, circumferential piston pumps and rotary lobe pumps are disclosed wherein a single gearbox module can be used with numerous heads of varying capacities and configurations. As a result, manufacturing costs are reduced because a single gearbox module with a drive shaft/driven shaft set can be used with numerous heads of varying capacities. Thus, the capacity can be varied without changing the gearbox or shaft length. Further, the mechanical shaft seals can be accessed for servicing or replacement without removal of the pump or rotor casing. Specifically, the mechanical shaft seals can be accessed merely by removal of the head cover plate and rotors, which are easily detachable from the drive and driven shafts.
2. Description of the Related Art
A positive displacement pump emits a given volume of fluid for each revolution of the motor or drive shaft. Bellows, double-diaphragm, flexible impeller, gear, oscillating, piston, progressing cavity, rotary vane, peristaltic, rotary lobe and circumferential piston pumps are all examples of positive displacement pumps. This disclosure is directed primarily towards new rotary lobe pump (RLP) and circumferential piston pump (CPP) designs. Both RLPs and CPPs employ a drive shaft and a driven shaft with rotors mounted on both shafts. The rotors are disposed in the pump casing sandwiched between a head cover and a gearbox. The head cover and rotor or pump casing are often collectively referred to as the “head” and the terms rotor casing and pump casing are used interchangeably.
Rotary lobe pumps use timing gears to eliminate contact between the rotors, which enables their use on non-lubricating fluids. Various rotor forms are available, including bi-wing (or bi-lobe) and multi-lobe options. These pumps offer both sanitary and hygienic designs which meet various standards imposed for food, dairy, beverage, bio-tech, and pharmaceutical applications. RLPs are also used in chemical and specialty chemical industries. Industrial RLP designs may include bearings on both sides of the rotors for higher pressure capabilities.
While circumferential piston pumps are timed like rotary lobe pumps, the rotor wings (i.e., the “pistons” in circumferential piston) rotate in chambers machined into the pump casing. This provides a large sealing surface which minimizes slip and provides increased efficiencies for low viscosity fluids. However, with the chambers machined into the pump casing, CPPs are significantly more difficult to clean and therefore can be less preferred for sanitary or hygienic applications.
In general, CPPs are preferred for lower viscosity liquids (less than 500 centipoise) and applications where cleaning and sanitization is not frequently needed; RLPs are preferred for higher viscosity liquids (greater than 500 centipoise) and sanitary or hygienic applications because of the ease in which an RLP can be cleaned.
One problem associated with both RLP and CPP designs is the inability to vary capacity without changing the overall pump design. Specifically, current RLP and the CPP designs require different gearboxes and shaft lengths for different capacities.
Another problem associated with RLP and CPP designs is the servicing of the mechanical shaft seals. Specifically, the mechanical shaft seals are traditionally mounted between the casing and a gearbox thereby requiring the head cover, rotors and casing to be removed in order to service the seals. This procedure is time-consuming and therefore costly. Accordingly, there is a need for improved CPP and RLP designs wherein access to the mechanical shaft seals is facilitated.